(1) Field of the Invention
This invention relates generally to a material and process for providing a protective corrosion inhibitor coating to an aluminum surface and relates specifically to a material and process for providing a cationic film corrosion inhibitor coating to the exposed aluminum surfaces of submarine weapons positioned in submarine torpedo tubes for launch.
(2) Description of the Prior Art
Since the introduction of high-strength aluminum alloys for construction of submarine weapons, a continuing problem has been seawater induced corrosion. As used herein, "aluminum" is considered to include aluminum and all aluminum alloys. Numerous attempts have been made to eliminate or minimize this corrosion problem but none have proven completely successful. Some of the techniques considered have included providing a paint or special coating on the weapons and/or the torpedo tubes, use of sacrificial anodes attached to the weapons during tube storage, and the use of premixed corrosion inhibitors in the torpedo tube to replace the conventional use of seawater. All of these methods have limitations and valuable weapon assets continue to be lost to the ravages of corrosion. Additionally, the repair of corrosion damage on the weapons is a time consuming and expensive liability.
Paint and coatings on the weapons suffer from the serious disadvantage of having their integrity broken by scratches and abrasions resulting from repeated tube loading and unloading evolutions. These scratches and abrasions, not only expose the bare aluminum but, also create an unfavorably large cathode-to-anode area ratio with the unpainted torpedo tubes which intensifies the corrosion reaction. Limited coating repair can be performed on the submarine or tender but the original integrity can never be fully restored without making extensive repairs to the weapons. At present, touch-up painting of the weapons, combined with routine preventive maintenance, is the primary corrosion prevention method.
Efforts to coat the interior of torpedo tubes with tar-based paints, to minimize the cathode-to-anode area ratio, have also been considered but no fully successful paint has been found that will maintain adhesion over a long period of time. The resulting paint chips damage the torpedo tube slide valve seals and, even when successful, painting of torpedo tubes is a difficult maintenance problem.
The use of sacrificial anodes, such as zinc and magnesium, attached to the weapon, has been shown to result in a significant reduction of corrosion levels. However, the resulting zinc and magnesium hydroxide precipitates cause serious problems in the operation of the torpedo tube slide valves and in the contamination of the submarine trim and drain system, and as a result, preclude this process from being used.
The use of corrosion inhibiting solutions in the weapon tubes instead of seawater has also been considered but never implemented because of the large volume required for the repeated flood down and draining evolutions which occur. Since space is at a premium on all submarines, there is currently no place to store the required large quantities of inhibitor solutions. Also, some trim and drain system modifications could be expected.